3 of 10

Hypothesis

Inside plants are tiny molecules called photopigments.

Photopigments help the plant absorb light. A plant has different

types of photopigments so it can absorb different colors of light.

White light or natural light has many different wavelengths or

colors of light in it so I believe that the plants will bend or grow

toward natural light more than plants exposed to only one color of light.

4 of 10

Materials

4- 1 foot tall cardboard boxes

12- bean seeds

12- small pots

3x3 piece of clear, red, green, and blue cellophane sheets

Spray bottle with water

Potting soil

5 of 10

Procedure

First, get plants growing by planting bean seeds in 4 pots
Cut a 2” hole in the front of each box
Place cellophane (1 of each color) to cover hole on each box
Position 1 plant in each box and measure that they are all the same distance in box
Place all boxes in equally lighted area
Keep all plants watered
Observe growth and record results
Repeat test x3

6 of 10

Conduct Experiment

Test was repeated 3 times. The results are conclusive with showing positive tropism in all plants however the plants only exposed to green light showed less growth and did not grow or bend toward the light. Needed to put plants into boxes earlier because growth before placing in boxes was rapid and plants grew too tall for the boxes and made it hard to get accurate results on all tests.

Test 1

Test 2

Test 3

7 of 10

Data Tables

Plants move toward the light. Seeds push little leaves up from the ground into the light. A house plant in a dark room will grow toward the light. This movement in response to light is called phototropism. When a plant moves toward the light, it’s called positive tropism. When a plant moves away from light, it’s called negative tropism.

8 of 10

Conclusion

The control plants did better than the rest of the plants and showed positive tropism. They were exposed to more colors of light vs. only one color of light. The plants exposed to the red and blue light were not far behind the control plants. The green plants grew the slowest or did not bend toward the light as the other plants did. The reason is that the green plant already reflects green light and the light will bounce off of the plant. This means that they can't use or absorb the light well.

Inside a plant are chloroplasts. Inside the chloroplasts are tiny molecules called photopigments. Photopigments help the plant absorb light. A plant has different photopigments so it can absorb different colors of light. When natural light shines on a plant, the plant takes in the light from different wavelengths and uses it to make food. This natural light is called white light and it contains all types of light. If there is only one color of light shining on a plant, then only some of the photopigments work and the plant doesn't grow as well. This is why the plant under the full light spectrum or the control plant grew better than the plans with the colored filters, especially the green filter.

Plants move with the help of chemicals called auxins. Auxins are like an elastic band for cells.

They help cells get longer and move. Sunlight reduces auxin, so the areas of the plant that are

exposed to sunlight will have less auxin. The areas on the dark side of the plant will have more

auxin. That means that they will have long, stretchy cells. This allows the plant to move toward

the light.

9 of 10

Real World Connections

When full spectrum light, like sunlight shines on a plant all the photopigments are activated and absorb their "specialty" color. A plant's chloroplasts get all the actions of the photopigments coordinated so that they're all working to harness most of the sun's light rays and make plant food.

If there is only one color of light shining on a plant, then only a certain group of photopigments are active. The plant won't be able to make as much sugar or plant food as when there is full spectrum light shining on it and it may suffer generally. Not only will the plant not have enough light to make lots of food, but the plant uses these different color lights to signal all sorts of other internal processes. If, for example, only blue light was shining on the plant, then all the red-light triggered processes would not occur.

Eventually the plant may die because of this lack of full spectrum light and certain processes not happening. It would be like in your body if suddenly your liver couldn't function anymore. Eventually you would die. So, plants need full spectrum (all the colors of the rainbow) light to live productively. This is why greenhouses and plant observation is important. We can control the growth of plants which can be important to sustain crops and food sources.

1 of 10

2 of 10